Four Chinese scammers are under arrest after their plot to fleece a poker-playing pigeon was rumbled.

On Sept. 23, a small business owner named Feng contacted police based on his suspicions that he’d been the victim of con men posing as fellow poker players. Feng claimed to have been drugged by the men before engaging in a marathon poker session in a hotel room in Dali, Yunnan province.

Police subsequently raided the hotel room, detaining the four suspects along with the tools of their trade: 30 packs of marked cards and a pair of specially designed contact lenses that allowed their wearer to identify the value of the cards via their markings on the back.

According to local media outlet Yunnan.cn, the suspects admitted their guilt, explaining that the individual who wore the contact lenses would use hand signals to tip off his three co-conspirators as to what cards Feng was holding.